Hf4+-exchanged montmorillonite-boosted Pd-catalyzed reductive aminolysis of aryl ethers to efficiently synthesize cyclohexylamines

Abstract

The construction of N-substituted amines from biomass-derived aryl ethers via reductive aminolysis is an emerging and highly attractive strategy for biomass valorization. However, realizing this transformation remains a great challenge over heterogeneous catalysts at a low H₂ pressure. Herein, we designed Hf-exchanged montmorillonite supported Pd nanoparticles (Pd/Hf-MMT) as a functional heterogeneous catalyst. Very interestingly, the fabricated Pd/Hf-MMT was highly efficient for the direct reductive aminolysis of aryl ethers with amines to synthesize various N-cyclohexyl-substituted amines at a low H₂ pressure of 0.3 MPa without using any homogeneous acidic additives. Systematic investigations revealed that the strong acidity of Hf-MMT and the lower electron density of metallic Pd synergistically resulted in the excellent activity of Pd/Hf-MMT. Notably, the Pd/Hf-MMT catalyst has great potential for practical applications because of some obvious advantages, such as low H₂ pressure, the heterogeneous nature, high efficiency, and broad substrate scope.